Junction-type active devices are readily implemented in bulk complementary-metal-oxide (CMOS) technologies and semiconductor-on-insulator (SOI) technologies. For example, bipolar junction transistors are formed by a pair of P-N junctions, namely an emitter-base junction and a collector-base junction. An NPN bipolar junction transistor has a thin region of P-type material constituting the base region between two regions of N-type material constituting the emitter and collector regions. A PNP bipolar junction transistor has a thin region of N-type material constituting the base region between two regions of P-type material constituting the emitter and collector regions. The movement of electrical charge carriers between the collector region and the emitter region, which produces electrical current flow, is controlled by a voltage applied across the emitter-base junction.
Conventional planar bipolar junction transistors, which are commonly implemented in radiofrequency integrated circuits, have a vertical arrangement of the emitter, base, and collector regions in which the emitter region is circumscribed by the base region and the collector region circumscribes the base region. As a result, the emitter and base regions of a bipolar junction transistor having a vertical architecture and must be situated between the collector region and a top surface of the substrate. For SOI substrates with thin device layers, the ability to maintain the vertical architecture of the bipolar junction transistor is lost. Conventional planar bipolar junction transistors also have a relatively large footprint that consumes a significant surface area of the SOI layer. The device footprint cannot be reduced because the area of the emitter-base junction cannot be easily scaled.
A semiconductor-controlled rectifier, which are also commonly implemented in radiofrequency integrated circuits, is a four-layer junction-type active device with a construction that is related to the construction of bipolar junction transistors. The construction of a semiconductor-controlled rectifier is similar in construction to a combination of two bipolar junctions that operate in conjunction to control device current flow. Consequently, semiconductor-controlled rectifiers face the same challenges as bipolar junction transistors for implementation in SOI technologies.
What is needed, therefore, are flexible methods for fabricating active junction-type active devices that overcome these and other deficiencies of conventional active junction-type active devices fabricated using an SOI technology substrate.